WASHINGTON — A top American diplomat signaled on Thursday that the United States might no longer demand that North Korea turn over a complete inventory of its nuclear assets as a first step in the denuclearization process that President Trump is pursuing.

The diplomat, Stephen E. Biegun, said in his first public speech that “before the process of denuclearization can be final, we must have a complete understanding of the full extent of the North Korean W.M.D. and missile programs through a comprehensive declaration.”

Mr. Biegun, appointed in August to be special representative for North Korea, was speaking to a room of North Korea experts at Stanford University. His reference to the timing of North Korea’s releasing a full list of its weapons of mass destruction indicates that the United States could be more flexible than it previously indicated about at what point in the negotiations the list is handed over.

If American negotiators drop their demand that the list is an essential first step in denuclearization, that would remove one obstacle that has hampered diplomacy since a summit meeting last June between Mr. Trump and Kim Jong-un, the North Korean leader.

Based on Mr. Biegun’s statement, the requirement now is that North Korea give international officials the list sometime before it ends its nuclear program for good, a process that could take years.

Mr. Trump said he planned to meet with Mr. Kim again in late February, despite the lackluster diplomacy and absence of any concrete sign that North Korea intends to stop its nuclear weapons program and rid itself of what American experts have estimated is a stockpile of 30 to 60 nuclear warheads.

Mr. Trump insists there has been some progress, and noted that North Korea has not conducted a nuclear test since September 2017.

On Thursday, Mr. Biegun stressed the same point.

“It has been more than 400 days since North Korea has undertaken a provocative test of a missile or a nuclear weapon,” he said. “Over the past year, North Korea has taken preliminary steps to dismantle and destroy the test sites used for these missile and nuclear tests.”

Mr. Biegun was referring to two sites to which Mr. Kim said he would allow outside experts access to verify their dismantlement or destruction. Some American analysts say the dismantlement can be reversed.

Mr. Biegun also reiterated the Trump administration’s position that it would “not lift sanctions until denuclearization is complete.” That has been one of the biggest points of contention between the United States and North Korea. Officials in Pyongyang have demanded that Washington scrap sanctions before denuclearization proceeds.

After last June’s summit meeting in Singapore, Mr. Trump posted on Twitter that “there is no longer a Nuclear Threat from North Korea.” No other American official has said that.

On Tuesday, U.S. intelligence agencies released an annual “Worldwide Threat Assessment” that said North Korea is unlikely to give up its nuclear stockpiles. Dan Coats, the national intelligence director, said in Senate testimony that the North’s “leaders ultimately view nuclear weapons as critical to regime survival.”

It is unclear what American negotiators would demand as an initial step for Pyongyang to prove it is committed to denuclearization, if the inventory of nuclear assets is delayed.

“Sequencing always confounds negotiators,” Mr. Biegun said after his speech in a question-and-answer session with Robert Carlin, a former intelligence analyst and policy adviser on North Korea.

Last October, the South Korean foreign minister, Kang Kyung-wha, told The Washington Post that it would be better to leave the inventory until later in the process. “If you start with a list and then get into a huge discussion about verification, you’re still working at that level of a lack of trust,” she said.

The leaders of the two Koreas have been engaged in diplomacy that has moved much faster than the talks between Washington and Pyongyang.